Bioavailability of Hydroquinone from Topical Formulations: A Product Comparison Study Using the in vitro Permeation Test

Introduction: The in vitro Permeation Test (IVPT) is considered to be an important tool for assessing the topical pharmacokinetics of dermatologic formulations. An IVPT study evaluating products that contain the skin bleaching agent, hydroquinone (HQ), as the active ingredient, is presented in support of the value of IVPT in comparing the relative bioavailability of HQ products from different commercial products. Methods: Ten former OTC and Rx products were evaluated for in vitro bioavailability using human ex vivo skin in Franz diffusion cells. In addition, to assess the correlation between in vitro and in vivo absorption, the suction blister technique was used to determine HQ concentration in interstitial fluid from two products differing in HQ bioavailability. Results: Significant differences in HQ absorption between products were found. Total absorption varied from 27 to 279 μg/cm2/48 h, and neither total absorption nor the rates of absorption were found to correlate with labeled drug concentration. In vivo suction blister data on the two products were in accordance with the IVPT results. Discussion: Overall, this study demonstrates the sensitivity and value of the IVPT method for detecting differences in the pharmacokinetics of topical formulations containing a single therapeutic agent but which differ in formulation design.